This invention relates to a phase distribution measurement method and apparatus, to a phase correction method and apparatus, and to a magnetic resonance imaging apparatus, and more specifically, to a method and apparatus for measuring the phase distribution in an image obtained by magnetic resonance imaging, to a method and apparatus for correcting the phase of pixel data based on the measured phase distribution, and to a magnetic resonance imaging apparatus which obtains water and lipid images based on the phase-corrected pixel data.
In a magnetic resonance imaging apparatus, a stationary magnetic field is formed in a space which accommodates an imaging object, a gradient magnetic field and a high frequency magnetic field are formed in the stationary magnetic field space, and an image is formed (reconstituted) based on a magnetic resonance signal generated by the spin of the imaging object. Due to a chemical shift, the magnetic resonance signal of lipids has a different frequency from the magnetic resonance signal of water, so water and lipids can be imaged separately using a phase difference based on the frequency difference.
The phase of the magnetic resonance signal is affected by the non-uniformity of the stationary magnetic field intensity, so in order to image water and lipids separately without being affected by the magnetic field non-uniformity a phase distribution, i.e. phase map, representing the stationary magnetic field non-uniformity, is calculated, and phase correction of the image is performed based thereon.
The phase map is obtained by calculating the phase of image data given by complex numbers for each pixel. FIG. 16 shows the concept of the phase map for a typical one-dimensional image. The origin of the phase map is taken as the center of the stationary magnetic field. The phase at the origin is 0.
This diagram is a phase map wherein the stationary magnetic field intensity has a linear gradient, and the phase varies linearly according to the distance from the origin. When the phase exceeds +xcfx80, it returns to the xe2x88x92xcfx80 aside, and when it exceeds xe2x88x92xcfx80, it returns to the +xcfx80 side, as shown by (a) in the figure. In other words, a phase wrap around takes place.
Therefore, in parts where there is a wrap around, a correction for wrap around, i.e. unwrapping, is performed to obtain a phase map without wrap around, as shown in (b). The presence or absence of a wrap around is detected by whether or not the absolute value of the phase difference of the image data for adjacent pixels is 2xcfx80, and for pixels where a wrap around is detected, 2xcfx80 is added to the phase with a reverse sign to that of the phase difference.
The phase map often comprises high order components due to the effect of noise or variation of magnetic susceptibility, etc., so as shown for example by FIG. 17(a), at a point A of the phase map, a phase difference which would have been 2xcfx80 may actually be less than this. Therefore, when it is attempted to detect a wrap around in the manner described above, a wrap around cannot be detected at points where it should have been detected, and the resulting phase map is inaccurate as shown in (b).
It is therefore an object of this invention, which was conceived to overcome the above problem, to provide a phase distribution measurement method and apparatus which efficiently calculate a precise phase map, a phase correction and apparatus using this calculated phase map, and a magnetic resonance imaging apparatus which performs such a phase correction.
(1) The invention from one aspect for solving the aforesaid problem is a phase distribution measurement method characterized by calculating the differentials of the phases of pixel data of an image obtained by magnetic resonance imaging for each pixel, calculating the integrals of the aforesaid differentials for each pixel, and forming a phase distribution from the aforesaid integrals.
In the invention according to this aspect, phase differentials are calculated for each pixel, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. In this way, a phase map is obtained in which unwrapping is performed naturally.
(2) The invention from another aspect for solving the aforesaid problem is a phase distribution measurement method characterized by filtering an image obtained by magnetic resonance imaging, calculating the differentials of the phases of pixel data for the filtered image, calculating the integrals of the differentials for each pixel, and forming a phase distribution from the integrals.
In the invention according to this aspect, phase differentials are calculated for each pixel, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. Before calculating the differentials, the image is filtered to obtain a phase map which is unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally.
(3) The invention from another aspect for solving the aforesaid problem is a phase distribution measurement method characterized by calculating the differentials of the phases of pixel data of an image obtained by magnetic resonance imaging for each pixel, filtering the differentials, calculating the integrals of the filtered differentials for each pixel, and forming a phase distribution from the aforesaid integrals.
In the invention according to this aspect, phase differentials are calculated for each pixel, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. After calculating the differentials, filtering is performed to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally.
(4) The invention from another aspect for solving the aforesaid problem is a phase distribution measurement method characterized by calculating the differentials of the phases of pixel data of an image obtained by magnetic resonance imaging or each pixel, calculating the integrals of the aforesaid differentials for each pixel, filtering the integrals, and forming a phase distribution from the aforesaid filtered integrals.
In the invention according to this aspect, phase differentials are calculated for each pixel, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. After calculating the integrals, filtering is performed to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally.
(5) The invention from another aspect for solving the aforesaid problem is a phase distribution measurement apparatus comprising a means for calculating the differentials of the phases of pixel data of an image obtained by magnetic resonance imaging for each pixel, a means for calculating the integrals of the aforesaid differentials for each pixel, and a means for forming a phase distribution from the aforesaid integral.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. In this way, a phase map is obtained in which unwrapping is performed naturally.
(6) The invention from another aspect for solving the aforesaid problem is a phase distribution measurement apparatus comprising a filtering means for filtering an image obtained by magnetic resonance imaging, a differential calculating means for calculating the differentials of the phases of pixel data for the filtered image, an integral calculating means for calculating the integrals of the differentials for each pixel, and a phase distribution forming means for forming a phase distribution from the integrals.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. Before calculating the differentials, the image is filtered by the filtering means to obtain a phase map which is unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally.
(7) The invention from another aspect for solving the aforesaid problem is a phase distribution measurement apparatus comprising a differential calculating means for calculating the differentials of the phases of pixel data of an image obtained by magnetic resonance imaging for each pixel, a filtering means for filtering the differentials, an integral calculating means for calculating the integrals of the filtered differentials for each pixel, and a phase distribution forming means for forming a phase distribution from the aforesaid integrals.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. After calculating the differentials, filtering is performed by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally.
(8) The invention from another aspect for solving the aforesaid problem is a phase distribution measurement apparatus comprising a differential calculating means for calculating the differentials of the phases of pixel data of an image obtained by magnetic resonance imaging for each pixel, an integral calculating means for calculating the integrals of the aforesaid differentials for each pixel, a filtering means for filtering the integrals, and a phase distribution forming means for forming a phase distribution from the aforesaid filtered integrals.
In the invention according to this aspect, phase differentials are calculated for each pixel by the phase differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. After calculating the integrals, filtering is performed by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally.
(9) The invention from another aspect for solving the aforesaid problem is a phase correction method characterized by calculating the differentials of the phases of pixel data of an image obtained by magnetic resonance imaging for each pixel, calculating the integrals of the differentials for each pixel, forming a phase distribution from the aforesaid integrals, and performing a phase correction of the image by the aforesaid phase distribution.
In the invention according to this aspect, phase differentials are calculated for each pixel, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected using this phase map.
(10) The invention from another aspect for solving the aforesaid problem is a phase correction method characterized by filtering an image obtained by magnetic resonance imaging, calculating the differentials of the phases of pixel data of the aforesaid filtered image, calculating the integrals of the differentials for each pixel, forming a phase distribution from the aforesaid integrals, and performing a phase correction of the image by the aforesaid phase distribution.
In the invention according to this aspect, phase differentials are calculated for each pixel, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. Before calculating the differentials, the image is filtered to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected using this phase map.
(11) The invention from another aspect for solving the aforesaid problem is a phase correction method characterized by calculating the differentials of the phases of the pixel data of an image obtained by magnetic resonance imaging for each pixel, filtering the differentials, calculating the integrals of the aforesaid filtered differentials for each pixel, forming a phase distribution from the aforesaid integrals, and performing a phase correction of the image by the aforesaid phase distribution.
In the invention according to this aspect, phase differentials are calculated for each pixel, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. After calculating the differentials, the image is filtered to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected using this phase map.
(12) The invention from another aspect for solving the aforesaid problem is a phase correction method characterized by calculating the differentials of the phases of the pixel data of an image obtained by magnetic resonance imaging for each pixel, calculating the integrals of the aforesaid differentials for each pixel, filtering the aforesaid integrals, forming a phase distribution from the aforesaid filtered integrals, and performing a phase correction of the image by the aforesaid phase distribution.
In the invention according to this aspect, phase differentials are calculated for each pixel, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. After calculating the integrals, filtering is performed to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected using this phase map.
(13) The invention from another aspect for solving the aforesaid problem is a phase correction apparatus comprising differential calculating means for calculating the differentials of the phases of the pixel data of an image obtained by magnetic resonance imaging for each pixel, an integral calculating means for calculating the integrals of the aforesaid differentials for each pixel, a phase distribution forming means for forming a phase distribution from the aforesaid integrals, and a phase correction means for performing a phase correction of the image by the aforesaid phase distribution.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected by the phase correction means using this phase map.
(14) The invention from another aspect for solving the aforesaid problem is a phase correction apparatus comprising a filtering means for filtering an image obtained by magnetic resonance imaging, a differential calculating means for calculating the differentials of the phases of the pixel data of the aforesaid filtered image for each pixel, an integral calculating means for calculating the integrals of the aforesaid differentials for each pixel, a phase distribution forming means for forming a phase distribution from the aforesaid integrals, and a phase correction means for performing a phase correction of the image by the aforesaid phase distribution.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. Before calculating the differentials, the image is filtered by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected by the phase correction means using this phase map.
(15) The invention from another aspect for solving the aforesaid problem is a phase correction apparatus comprising a differential calculating means for calculating the differentials of the phases of the pixel data of an image obtained by magnetic resonance imaging for each pixel, a filtering means for filtering the aforesaid differentials, an integral calculating means for calculating the integrals of the aforesaid filtered differentials for each pixel, a phase distribution forming means for forming a phase distribution from the aforesaid integrals, and a phase correction means for performing a phase correction of the image by the aforesaid phase distribution.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. After calculating the differentials, the image is filtered by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected by the phase correction means using this phase map.
(16) The invention from another aspect for solving the aforesaid problem is a phase correction apparatus comprising a differential calculating means for calculating the differentials of the phases of the pixel data of the image obtained by magnetic resonance imaging for each pixel, an integral calculating means for calculating the integrals of the aforesaid differentials for each pixel, a filtering means for filtering the aforesaid integrals, a phase distribution forming means for forming a phase distribution from the aforesaid filtered integrals, and a phase correction means for performing a phase correction of the image by the aforesaid phase distribution.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. After calculating the integrals, the image is filtered by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected by the phase correction means using this phase map.
(17) The invention from another aspect for solving the aforesaid problem is a magnetic resonance imaging apparatus comprising an imaging means for forming an image of each imaging object using magnetic resonance, a differential calculating means which calculates the differentials of the phases of the pixel data of the aforesaid image for each pixel, an integral calculating means which calculates the integrals of the aforesaid differentials for each pixel, a phase distribution forming means which forms a phase distribution from the aforesaid integrals, a correction means which performs a phase correction of the image by the aforesaid phase distribution, and an image-forming means for separately generating a water image and a lipid image using the phase differences of pixel data of the phase-corrected image.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected by the phase correction means using this phase map. Water and lipids are separately imaged by the image generating means based on the phase-corrected image data.
(18) The invention from another aspect for solving the aforesaid problem is a magnetic resonance imaging apparatus comprising imaging means for forming an image of each imaging object using magnetic resonance, a filtering means for filtering the aforesaid image, a differential calculating means for calculating the differentials of the phases of the pixel data of the aforesaid filtered image for each pixel, an integral calculating means for calculating the integrals of the aforesaid differentials for each pixel, a phase distribution forming means for forming a phase distribution from the aforesaid integrals, a phase correction means for performing a phase correction of the image by the aforesaid phase distribution, and an image-forming means for separately generating a water image and a lipid image using the phase differences of the pixel data of the phase-corrected image.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. Before calculating the differentials, the image is filtered by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected by the phase correction means using this phase map. Water and lipids are separately imaged by the image generating means based on the phase-corrected image data.
(19) The invention from another aspect for solving the aforesaid problem is a magnetic resonance imaging apparatus comprising an imaging means for forming an image of each imaging object using magnetic resonance, a differential calculating means for calculating the differentials of the phases of the pixel data of the aforesaid filtered image for each pixel, a filtering means for filtering the aforesaid differentials, an integral calculating means for calculating the integrals of the aforesaid filtered differentials for each pixel, a phase distribution forming means for forming a phase distribution from the aforesaid integrals, a phase correction means for performing a phase correction of the image by the aforesaid phase distribution, and an image-forming means for separately generating a water image and a lipid image using the phase differences of the pixel data of the phase-corrected image.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. After calculating the differentials, the image is filtered by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected by the phase correction means using this phase map. Water and lipids are separately imaged by the image generating means based on the phase-corrected image data.
(20) The invention from another aspect for solving the aforesaid problem is a magnetic resonance imaging apparatus comprising an imaging means for forming an image of each imaging object using magnetic resonance, a differential calculating means for calculating the differentials of the phases of the pixel data of the aforesaid image for each pixel, an integral calculating means for calculating the integrals of the aforesaid differentials for each pixel, a filtering means for filtering the aforesaid integrals, a phase distribution forming means for forming a phase distribution from the aforesaid integrals, a phase correction means for performing a phase correction of the image by the aforesaid phase distribution, and an image-forming means for separately generating a water image and a lipid image using the phase differences of the pixel data of the phase corrected image.
In the invention according to this aspect, phase differentials are calculated for each pixel by the differential calculating means, corresponding integrals are calculated for each pixel by the integral calculating means, and a phase map is formed from the integrals by the phase distribution forming means. After calculating the integrals, the image is filtered by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected by the phase correction means using this phase map. Water and lipids are separately imaged by the image generating means based on the phase-corrected image data.
(21) The invention from another aspect for solving the aforesaid problem is a magnetic resonance imaging method characterized by forming an image using magnetic resonance for each imaging object, calculating the differentials of the phases of the pixel data of the image formed for each pixel, calculating the integrals of the aforesaid differentials for each pixel, forming a phase distribution from the aforesaid integrals, performing a phase correction of the image by the aforesaid phase distribution, and separately generating a water image and a lipid image using the phase differences of the pixel data of the phase-corrected image.
In the invention according to this aspect, phase differentials are calculated for each pixel for each image obtained by magnetic resonance imaging, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected using this phase map. Water and lipids are separately imaged by the image generating means based on the phase-corrected image data.
(22) The invention from another aspect for solving the aforesaid problem is a magnetic resonance imaging method characterized by forming an image using magnetic resonance for each imaging object, filtering the image, calculating the differentials of the phases of the pixel data of the filtered image formed for each pixel, calculating the integrals of the aforesaid differentials for each pixel, forming a phase distribution from the aforesaid integrals, performing a phase correction of the image by the aforesaid phase distribution, and separately generating a water image and a lipid image using the phase differences of the pixel data of the phase-corrected image.
In the invention according to this aspect, phase differentials are calculated for each pixel for each image obtained by magnetic resonance imaging, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. Before calculating the differentials, the image is filtered to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected using this phase map. Water and lipids are separately imaged by the image generating means based on the phase-corrected image data.
(23) The invention from another aspect for solving the aforesaid problem is a magnetic resonance imaging method characterized by forming an image using magnetic resonance for each imaging object, calculating the differentials of the phases of the pixel data of the image formed for each pixel, filtering the differentials, calculating the integrals of the aforesaid filtered differentials for each pixel, forming a phase distribution from the aforesaid integrals, performing a phase correction of the image by the aforesaid phase distribution, and separately generating a water image and a lipid image using the phase differences of the pixel data of the phase-corrected image.
In the invention according to this aspect, phase differentials are calculated for each pixel for each image obtained by magnetic resonance imaging, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. After calculating the differentials, filtering is performed by the filtering means to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected using this phase map. Water and lipids are separately imaged by the image generating means based on the phase-corrected image data.
(24) The invention from another aspect for solving the aforesaid problem is a magnetic resonance imaging method characterized by forming an image using magnetic resonance for each imaging object, calculating the differentials of the phases of the pixel data of the image formed for each pixel, calculating the integrals of the aforesaid differentials for each pixel, filtering the integrals, forming a phase distribution from the aforesaid filtered integrals, performing a phase correction of the image by the aforesaid phase distribution, and separately generating a water image and a lipid image using the phase differences of the pixel data of the phase-corrected image.
In the invention according to this aspect, phase differentials are calculated for each pixel for each image obtained by magnetic resonance imaging, corresponding integrals are calculated for each pixel, and a phase map is formed from the integrals. After calculating the integrals, filtering is performed to obtain a phase map unaffected by noise. In this way, a phase map is obtained in which unwrapping is performed naturally. The image data is phase-corrected using this phase map. Water and lipids are separately imaged by the image generating means based on the phase-corrected image data.
As described in detail above, according to this invention, a phase distribution measurement method and apparatus for efficiently calculating a precise phase map, a phase correction method and apparatus using the phase map thus calculated, and a magnetic resonance imaging apparatus which performs this phase correction, can be obtained.